Pull up following revision(s) (requested by roy in ticket #724):
tests/net/icmp/t_ping.c: revision 1.19
sys/netinet6/raw_ip6.c: revision 1.166
sys/netinet6/ip6_input.c: revision 1.195
sys/net/raw_usrreq.c: revision 1.59
sys/sys/socketvar.h: revision 1.151
sys/kern/uipc_socket2.c: revision 1.128
tests/lib/libc/sys/t_recvmmsg.c: revision 1.2
lib/libc/sys/recv.2: revision 1.38
sys/net/rtsock.c: revision 1.239
sys/netinet/udp_usrreq.c: revision 1.246
sys/netinet6/icmp6.c: revision 1.224
tests/net/icmp/t_ping.c: revision 1.20
sys/netipsec/keysock.c: revision 1.63
sys/netinet/raw_ip.c: revision 1.172
sys/kern/uipc_socket.c: revision 1.260
tests/net/icmp/t_ping.c: revision 1.22
sys/kern/uipc_socket.c: revision 1.261
tests/net/icmp/t_ping.c: revision 1.23
sys/netinet/ip_mroute.c: revision 1.155
sbin/route/route.c: revision 1.159
sys/netinet6/ip6_mroute.c: revision 1.123
sys/netatalk/ddp_input.c: revision 1.31
sys/netcan/can.c: revision 1.3
sys/kern/uipc_usrreq.c: revision 1.184
sys/netinet6/udp6_usrreq.c: revision 1.138
tests/net/icmp/t_ping.c: revision 1.18
socket: report receive buffer overflows
Add soroverflow() which increments the overflow counter, sets so_error
to ENOBUFS and wakes the receive socket up.
Replace all code that manually increments this counter with soroverflow().
Add soroverflow() to raw_input().
This allows userland to detect route(4) overflows so it can re-sync
with the current state.
socket: clear error even when peeking
The error has already been reported and it's pointless requiring another
recv(2) call just to clear it.
socket: remove now incorrect comment that so_error is only udp
As it can be affected by route(4) sockets which are raw.
rtsock: log dropped messages that we cannot report to userland
Handle ENOBUFS when receiving messages.
Don't send messages if the receiver has died.
Sprinkle more soroverflow().
Handle ENOBUFS in recv
Handle ENOBUFS in sendto
Note value received. Harden another sendto for ENOBUFS.
Handle the routing socket overflowing gracefully.
Allow a valid sendto .... duh
Handle errors better.
Fix test for checking we sent all the data we asked to.

(bouyer)